Wood nanobattery could be green option for large-scale energy storage

Li-ion batteries may be ok for your smartphone, but when it comes to large-scale energy storage, the priorities suddenly shift from compactness and cycling performance (at which Li-ion batteries excel) to low cost and environmental feasibility (in which Li-ion batteries still have much room for improvement). A new "wood battery" could allow the emerging sodium-ion battery technology to fit the bill as a long-lasting, efficient and environmentally friendly battery for large-scale energy storage.

Scientists are speculating that sodium-ion batteries, currently in an early stage of development, could suit large-scale energy storage much better than Li-ion batteries, partially because sodium is cheap and plentiful and because sodium is environmentally benign. But for Na-ion batteries to become a viable energy-storage option there are still many obstacles to overcome, the greatest of which is the phenomenon known as sodiation.

With each charge/discharge cycle, the sodium ions cause the anode of the battery to swell by as much as 420 percent and then return to normal. This phenomenon, known as sodiation, can literally pulverize the anode after only 20 cycles, rendering the battery extremely short-lived. University of Maryland (UM) researchers Liangbing Hu and Teng Li found a way around this problem.

The stiff bases often used in existing batteries are too brittle to withstand the swelling and shrinking caused by sodiation, so the researchers turned to the much softer wood fibers. These have evolved to withstand these forces extremely well as they use capillary forces to transfer the sodium ions from the soil around them to the leaves of their tree. The resulting sodium-ion battery that uses wood fibers increases durability twenty-fold compared with previous designs.

The researchers coated a sliver of wood fibers with a thin layer (10 nm) of single-walled carbon nanotubes to make it electrically conductive, and then deposited a tin film over it. The soft wood fibers effectively neutralized the strong mechanical stresses of the sodiation process: Even after charging and discharging the battery hundreds of times, the wood ended up wrinkled but remarkably intact.

"Pushing sodium ions through tin anodes often weaken the tin’s connection to its base material," said Li, an associate professor of mechanical engineering. "But the wood fibers are soft enough to serve as a mechanical buffer, and thus can accommodate tin’s changes. This is the key to our long-lasting sodium-ion batteries."

"Wood fibers that make up a tree once held mineral-rich water, and so are ideal for storing liquid electrolytes, making them not only the base but an active part of the battery," added Hu.

In their testing, the researchers measured a stable cycling performance of 400 cycles with an initial capacity of 339 mAh/g, which is a marked improvement over previous designs.

Because sodium doesn't store energy quite as efficiently as lithium, there is little chance of this technology eventually finding its way to your next-generation gadget. However, because of their low cost and use of environmentally benign common materials, sodium-ion batteries could be used to store large amounts of energy from renewable energy sources, such as wind and solar.

A paper detailing the research was published on the journal Nano Letters.

Dario studied software engineering at the Polytechnic University of Turin. When he isn't writing for Gizmag he is usually traveling the world on a whim, working on an AI-guided automated trading system, or chasing his dream to become the next European thumbwrestling champion. All articles by Dario Borghino

Would this be green because farmers would suddenly start raising a lot of trees or would a lot of forest be cut down even if new 1 foot tall saplings are put in the place of trees that take 100+ years to grow?

Mitko Ian 6th July, 2013 @ 10:30 pm PDT

@Mitko Ian:

Loss of forest is a problem in developing countries, not the 'West'.

Forestry coverage in the US and Western World is significantly higher now than it has been in the past seventy years.

This is because timber companies manage their assets so as not to deplete their own inventory.

Also, not sure where you get the 100+ years from....

...there are plenty of fast growth trees that reach maturity within ten years, and when effectively managed (see para above) present no problem to sustainability at all.

Robt 7th July, 2013 @ 01:11 am PDT

why this obsession with storing wind and solar power ? they are such a tiny percentage of power production today that we can always use what little they do produce immediately on the grid ... If you are thinking about off grid then you don't need special new batteries to handle that ...

Jeffrey J Carlson 7th July, 2013 @ 08:06 am PDT

Could be used to store large quantities of energy by energy resources. I assume you mean "Power Companies" that own renewable producing apparatus ie windmills, large solar farms, etc. I'm not sure if they would want to do this. After all it would leave a trail to the power companies and how well they are collecting power for free and then selling it back to the suckers who gave them the power in the first place.

Store the hydroelectric power made during the day, and then sell it back to the "suckers" at night. What a sweet deal. LOL

S Michael 7th July, 2013 @ 03:08 pm PDT

Interesting but we could build pneumatic energy storage today with a few advantages as well. Such as if you were to put a catalytic filter just after the compressor the discharged air could be significantly less polluted that the intake air. Also you should harvest the generated heat and cold but the same Stirling cycle can be used in both phases of the operation.

Slowburn 7th July, 2013 @ 04:57 pm PDT

Engines have a peak efficiency output level, run them at more or less output and they burn more fuel per output. Gas turbines burn almost as much fuel idling as they do running at power.

If your storage system is efficient enough running the engines at max efficiency constantly and matching the load by charging or discharging the "battery" you can come out ahead.

Because the industrial price of electricity varies with demand it is possible to buy electricity when the price is low and pump water up a hill and when demand and price is high sell electricity that you generated by running the water down the hill and make a profit.

Wind, solar, tidal, waves and etc. can only produce when available so if it is going to be the primary generating capacity energy storage is a must. Also the "battery" can be fed untamed electricity full of spikes and dips and deliver smooth current. Wind turbines in particular should directly pump water or air into a storage tank and the electricity generated on demand from the "battery".

Slowburn 8th July, 2013 @ 05:26 am PDT

I think this would make going green even greener; IMO.

BigGoofyGuy 8th July, 2013 @ 09:16 am PDT

I agree with the statement that compactness is not as big a consideration on grid scale storage but aren’t number of cycles important when it comes to determining ROI and grid application feasibility?

What defines a cycle? Is it 80%+ depth of discharge? Maybe sheer capacity can make up for full cycles as a large enough battery does not need to be drawn down as much to supply ancillary services like regulation.